offs predicted by the model. An alternative approach is to define a recursive utility function. In this specification, service users are reluctant to change their expected consumption of the service over time. Recursive utility is time consistent and can be combined with a subjective rate of discount and risk aversion. However, it is not often used because of the mathematical complexity of the function.

Getting consistent contingent valuation responses is complicated when one asks consumers to estimate future values for different generations. An indirect method of valuation can be performed by defining the current economic restrictions and reallocations that are needed to ensure future viability. By measuring the opportunity cost of these constraints on the economic system, we can measure a lower bound value that is currently politically acceptable.

In summary, the economic valuation of the wide range of ecosystem services provided by rivers presents many problems because of both the lack of market signals for many of the services and the difficulty in assigning direct causal effects to inputs into complex and interdependent ecosystems. However, there is a wide range of approaches that can provide reasonable valuations for many services and at least a consistent ordering of relative values for those services that are more difficult to value.

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